1. Field of the Invention
The present invention relates to a gas collecting device capable of collecting a gas existing in an inner space of a coolant container for containing and cooling a heating element, and a test head and an IC device testing apparatus provided with the gas collecting device.
2. Description of the Related Art
Some elements composing an electric circuit are those which generate heat (heating elements) due to their operations, such as an IC device. Particularly in recent years, along with an operation speed getting higher and an integrated circuit getting highly densified, a heat value of an IC device has increased and demands for effectively cooling the IC device have become stronger. For example, in an LSI device mount device wherein a large number of LSI are modularized and mounted on one or both surfaces of a print substrate, the LSI device on the substrate generating heat due to its operation has to be cooled.
Therefore, a heating element mount device has been developed, wherein a plurality of heating elements mounted on a substrate are covered with a sealing case and a coolant circulates by a predetermined route in the sealing case (for example, the Japanese Unexamined Patent Publication No. 10-51169 and the Japanese Unexamined Patent Publication No. 10-303586).
In such a heating element mount device, when gas accumulation generates in the coolant route, heating elements in that part cannot be cooled. Therefore, to prevent generation of gas accumulation, it is general that a coolant inlet portion is provided at a lower portion of the sealed case and a coolant outlet portion is provided at an upper portion of the sealed case to flow the coolant from the bottom to top and an air existing in the coolant route is discharged with the coolant by utilizing own buoyancy.
However, even after a certain time from start of coolant circulation, an air or bubble may remain in a narrow part of an electric component and substrate. For example, an air or bubble tends to remain in a narrowly pitched IC lead part and a space between an electric component and a substrate, etc. In this case, it takes a long time to discharge the air or bubble to a degree that a test can be conducted. Also, since there are varying factors, such as a heating condition of the heating element, etc. other than a flow rate, temperature and viscosity of the coolant, the gas accumulation that an air or bubble stay may be hard to be eliminated in some cases even when partition walls are suitably designed.
IC devices adjacent to a gas accumulation as above is under a different cooling condition from a predetermined condition and the internal temperature changes, so that a signal propagation delay amount of the IC internal circuit changes along with the change of the internal temperature. As a result, in a system requiring timing accuracy of a testing apparatus, particularly in an IC device testing apparatus, there arises a problem that timing accuracy becomes deteriorated or unstable.